BC351 CH12-14 Practice Problems

Per unit mass, which will produce the most ATP?

16-carbon saturated fatty acid

Succinate dehydrogenase: - binds and releases the diffusible coenzyme FAD/FADH2. - is found in the aqueous environment of the mitochondria. - is regulated by NADH and ATP. - products will account for the production of 5 mols of ATP via every mol of glucose oxidized. - None of the above.

None of the above

Pyruvate dehydrogenase complex is a large enzyme complex comprised of 3 subunits and a number of coenzymes. Which of the following statements regarding this enzyme is true?

ALL OF THE ABOVE: - The redox reaction this enzyme catalyzes stores free energy in a thioester bond. - Lipoate, one of the enzymes coenzymes, is a lipid derivative that participates in redox chemistry via a disulfide bond. - Contains FAD that undergoes a reduction and oxidation prior to the end of the catalytic mechanism. - Decarboxylates pyruvate.

- citric acid cycle: - Lipoate: - TPP: - amphibolic: - Coenzyme A: - PDH complex:

- citric acid cycle: oxidizes acetyl-CoA - Lipoate: coenzyme that carries electrons between subunits in the PDH complex. - TPP: coenzyme that facilitates at least two different decarboxylation reactions in cellular respiration. citrate synthase:exhibits an induced fit. oxidative carboxylation:oxidation reaction in which a carbon is removed as CO2. - amphibolic: exhibiting both catabolic and anabolic characteristics. - Coenzyme A: coenzyme that will form high-energy thioester bonds with ketoacid compounds. - PDH complex: oxidizes pyruvate

Acetyl-CoA and succinyl-CoA store free energy from redox reactions that:

- in the case of acetyl-CoA, drives the reaction catalyzed by citrate synthase driving down oxaloacetate concentrations. - in the case of succinyl-CoA, leads to substrate-level phosphorylation.

What is the gross molar amount of NADH, FADH2, and ATP equivalents produced in the first two phases of cellular respiration for the oxidation of 1 mol of glucose? Name the enzymes that make each product and how much they make per mol of glucose.

2 mols of NADH from GAPDH (glycolysis), 2 mols of NADH from PDH, 2 mols of NADH from isocitrate dehydrogenase, 2 mols of NADH from α-KGA dehydrogenase, 2 mols of NADH from malate dehydrogenase making for a total of 10 mols of NADH. 2 mols of ATP from phosphoglycerate kinase (glycolysis), 2 mols of ATP from pyruvate kinase (glycolysis), and 2 mols of GTP (ATP equivalent) from succinyl-CoA synthetase making for a total of 6 mols of ATP equivalents (gross). 2 mols of FADH2 from succinate dehydrogenase.

Which of the following statements is true concerning the succinate dehydrogenase reaction?

An alkane to alkene transition like this is usually coupled to FAD reduction/oxidation.

Which is true regarding fatty acids containing an equal number of carbons?

Unsaturated fatty acids store less energy than saturated fatty acids since unsaturated fatty acids are more oxidized.

Carnitine shuttle, Malonyl-CoA, Carnitine acyltransferase 1, PPARα

Carnitine shuttle: rate-limiting step of fatty acid oxidation Malonyl-CoA: accumulates when an animal is well-supplied with carbohydrate Carnitine acyltransferase 1: inhibited by malonyl-CoA PPARα: transcription factor that activates β-oxidation

If stearic acid (18:0) is to be oxidized to acetyl-CoA via β-oxidation (Chapter 14), how many rounds of this metabolic process are required?

Eight rounds of β-oxidation will be required since each round will release two carbons as one molecule of acetyl-CoA. The last two carbons of stearic acid will remain as acetyl-CoA.

Which coenzyme(s) is(are) required for β-oxidation?

FAD, NAD+ and CoA-SH

In 1946 fluoroacetate was introduced as a rodenticide (rat poison) after which many farmyard animals died due to ingestion. Attempts to make an antidote for rat poison included treatment with acetate that did alleviate symptoms however were not entirely effective. Explain the rationale behind why acetate may act as an antidote for rat poison ingestion.

Fluoroacetate is harmless unless acted upon by acetate thiokinase leading to the production of fluoroacetyl-CoA that is then acted upon by citrate synthase making 2-fluorocitrate that is a potent inhibitor of aconitase. By feeding patients with large amounts of acetate the hope is that thiokinase will preferentially bind to acetate allowing fluoroacetate to be harmlessly secreted.

Which of the following metabolic processes occurs under anaerobic and aerobic conditions?

Glycolysis

Which of the following enzymes leads to NADH formation and catalyzes an irreversible step?

Isocitrate dehydrogenase

Lipids, Unsaturated fatty acids, Saturated fatty acids, Acetyl-CoA

Lipids: contain long alkyl chains Unsaturated fatty acids: contain at least one carbon-carbon double bond Saturated fatty acids: contain only carbon-carbon single bonds Acetyl-CoA: a product of β-oxidation

Beriberi is a disease caused by vitamin B1 deficiency resulting in fatigue, swelling of the hands and feet, shortness of breath, confusion, and spastic eye movement. One of the markers of this disease is an elevated level of pyruvate in the blood stream. Why might this be the case?

Pyruvate is the product of both carbohydrate and amino acid catabolism that enters cellular respiration in the mitochondria when converted to acetyl-CoA catalyzed by the PDH complex. The first step in the PDH complex reaction is a decarboxylation reaction that cannot be catalyzed without the enzyme thiamine pyrophosphate or TPP. This coenzyme is a derivative of thiamine or vitamin B1. An individual that has a thiamine deficiency will not efficiently metabolize pyruvate leading to elevated levels of it in the blood stream.

How many molecules of ATP will be produced in a human if one molecule of stearic acid (18:0) is completely oxidized to carbon dioxide and water via β-oxidation (Chapter 14) and the citric acid cycle (Chapter 12) assuming the reduced electron carriers generated in the citric acid cycle donate their electrons to the electron transport chain (Chapter 13)?

The Summation of ATP Produced in the Complete Oxidation of Stearic Acid Enzyme Catalyzing ReactionSubstrates Used or Products formed affecting ATPAccumulation of ATP β-Oxidation Acyl-CoA synthetase-1 ATP-2*Acyl-CoA dehydrogenase8 FADH212β-Hydroxyacyl-CoA dehydrogenase8 NADH20Citric Acid Cycle Isocitrate dehydrogenase9 NADH22.5α-Ketoglutarate Dehydrogenase9 NADH22.5Succinyl-CoA synthetase9 GTP9Succinate dehydrogenase9 FADH213.5Malate dehydrogenase9 NADH22.5 Total 120 *Because this reaction breaks both of ATP's phosphoanhydride bonds, the energetic cost is equivalent to 2 ATP.

From your knowledge of the structure of triacylglycerols (Chapter 9) and β-oxidation (Chapter 14), which portion of the triacylglyerol stores the largest amount of energy?

The fatty acid portions store the largest amount of free energy since the carbons are more reduced in these portions than the glycerol portion. See Chapter 10 for a review on the oxidation states of carbon.

If you were to purify, from the cell, all 8 enzymes of the citric acid cycle and combine them in a single reaction vessel what substrates would you need to add to run the entire cycle? Note: The purification process removed all low molecular weight molecules except coenzymes.

You would need to added acetyl-CoA, oxaloacetate, GDP (or ADP), and Pi. From these four compounds the entire cycle could run.

The reactions of the citric acid cycle:

are oxygen dependent

Cellular respiration:

is oxygen dependent

The citric acid cycle, also known as the Kreb's Cycle.

plays roles in both catabolism and anabolism